Mammalian lungs are vulnerable to the damaging effects of oxidative stress consequent to exposure to a wide variety of agents. Drugs, xenobiotics, hyperoxia and activated phagocytes are common and clinically important sources of oxidative damage and function loss in lungs. Toxic oxidative stress engendered by drugs (quinone derivatives and nitrofurantoin) and xenobiotics (paraquat) hyperoxia and stimulated neutrophils appears to originate from partially reduced oxygen moieties, including hydrogen peroxide and the oxygen free radicals, superoxide anion and the hydroxyl radical. Endothelial cells of the pulmonary microvasculature are the initial target of oxidative assault from hyperoxia and activated neutrophils. Although the cellular site of damage and initiating agents have been identified, no clear picture has emerged of the molecular sequence or reversibility of events which occur after initiation. Peroxidative cleavage of membrane lipids, DNA strand breakage, protein destruction, nucleotide loss and glutathione depletion have all been invoked to explain cell necrosis. Using a model cell system composed of pulmonary endothelial cells grown to confluence, preliminary data have been collected showing that superoxide dismutase and catalase provide protection against oxidative stress produced chemically or by activated neutrophils. Proposed studies will use cells from pulmonary artery, pulmonary vein and the microvasculature grown to confluence in monolayers. Pyridine nucleotide content and redox balance, nucleotide turnover, bioamine transport and metabolism (as a measure of specific endothelial cell function); and the glutathione peroxidase system will be determined in these cells. Preliminary data recently collected demonstrates that nicotinamide protects both endothelial cells in culture and animal lungs in situ when each is subjected to oxidative stress. Because nicotinamide is known to inhibit the enzyme poly ADP-ribose synthetase, these results hint that poly ADP-ribosylation may be involved in the toxic events consequent to oxygen radical attack. Radiolabeled precursors to the substrate NAD will be used to assess this possibility. It is hoped that by understanding the nature and sequence of toxic events following oxidative stress, the clinically important problems of lung damage related to hyperoxic and drug therapy as well as chronic inflammatory conditions can be better understood. A rational understanding of the underlying molecular events may aid in developing rational treatments to prevent cell damage.